Capacitive touchpad is an input device that allows user to slide his finger on a smooth panel thereof for cursor movement control. Because of its very small thickness, capacitive touchpad can be designed in slim notebooks, keyboards, digital media players and other devices, and moreover, due to its non-mechanical design it is virtually maintenance free.
FIG. 1 shows a cross-sectional view of a conventional two-dimensional capacitive touchpad 100, which comprises a panel 102, a Y-axial sensing layer 104, an insulating layer 106, an X-axial sensing layer 108, and a bottom plate 110. When a finger 112 touches on the panel 102, the sensed values (to the capacitances of the traces in the touchpad 100) on the touched position will vary, and the control circuit connected to the touchpad 100 can convert the sensed capacitive variation on the touchpad 100 to a sensed value as shown in FIG. 2, by which the position where the finger 112 touches and the moving distance and the moving direction of the finger 112 can be determined. Conventionally, there are two methods to determine whether an object touches on the touchpad 100. In the first method, the sensed value on the touchpad 100 is used to determine if an object touches the touchpad 100 by the way as shown in FIG. 3. When the sensed value is greater than a threshold th, it is determined that an object touches on the touchpad 100, and on the contrary, when the sensed value is less than the threshold th, it is determined that the object leaves the touchpad 100 or no object touches on the touchpad 100. In the second method, the cumulative sensed value on the touchpad 100 is used to determine if an object touches on the touchpad 100 by the way as shown in FIG. 4, by which if the cumulative sensed value is greater than a threshold th, it is determined that an object touches on the touchpad 100, otherwise it is determined that the object leaves the touchpad 100 or no object touches on the touchpad 100. However, these two detection methods might be interfered by external noise, which will cause erroneous determination and accordingly operation that is not desired or predicted. Moreover, the operation of drag gesture on the touchpad 100 is determined based on the time relationship when an object operates to fall down to the touchpad 100, leave from the touchpad 100, and move on the touchpad 100, and thus, for a user using the touchpad 100 first time or being unfamiliar with operating the touchpad 100, the action of the user might not be so definite that the touchpad 100 will detect thereto incorrectly and cause inconvenient use. In addition, with the trend of reducing the size of electronic products, the size of the touchpad 100 also needs to reduce. It results in inconvenience that the drag is often over the range of the touchpad 100 and thus the user needs to repeat the operation several times for a wide drag range.
Therefore, it is desired a detection method for a touchpad that will avoid noise to interfere the operation of the touchpad and have the touchpad to be easy to operate with.